White balance is the process of removing unrealistic color cast from a digital image caused by the color of the illumination. Human eyes automatically adapt to the color of the illumination, such that white will always appear white. Unfortunately, image capture devices (e.g., camera sensors) cannot adapt automatically. Therefore, white balance techniques are needed for imaging sensors in image capture systems (e.g., a digital camera) to compensate for the effect of illumination.
Automatic white balance (AWB) is an essential part of the imaging system pipeline in image capture systems. Digital still cameras and camera phones, for example, apply AWB techniques to correctly display the color of digital images. The quality of AWB has been a differentiating factor for different camera brands.
Typical scenes in photographs and videos may include expanses of sky, trees, grass, sand, sea, and/or people. Such scenes may have large areas of dominant object color: blue, green, yellow, etc. The unique combination of these colors may occur in specific scenes, for instance, blue+yellow→beach scene (sky, sea, and sand); blue+green→outdoor landscape (sky, tree, and grass), etc. Such scenes may be difficult to render in many image capture systems because commonly used white balance techniques may mistake a dominant object color for color cast from the illuminant, and hence try to neutralize the object color to reduce color cast. This leads to inaccurate color in the image or creation of false color cast in the image. Accordingly, improvements in automatic white balance in order to improve the quality of digital images captured by image capture systems are desirable.